Field test apparatus for analysis of coolants and heat-exchange fluids

ABSTRACT

A test method and apparatus for determining the content of carboxylic acid-based corrosion inhibitors in a coolant or heat exchange fluid. The amount of acidic reagent added to the coolant or fluid between two pH equilibrium points is measured to determine the amount of inhibitors. The refractive index can be measured to determine the amount of freezing point depressant.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a method and apparatus for testing thequality of engine coolants and heat-exchange fluids. More particularly,this invention relates to a field test, requiring a minimum of operatorinteraction.

[0003] 2. Related Art

[0004] Recently Organic Acid Technology (OAT) coolants and heat exchangefluids have been introduced commercially, and provide improved corrosionprotection and long life. OAT corrosion inhibitor packages in aqueousand glycol concentrates are used in automotive, heavy duty, marine andindustrial applications. OAT inhibitors are also used in secondarycooling systems and in a variety of industrial heat exchange fluids. Theuse of monocarboxylic or dicarboxylic acids, or the salts of such acids,as corrosion inhibitors in antifreeze/coolant and heat-exchange fluidcompositions is disclosed for instance in EP-A-0 479 470,-0 564 721 and—0 573 287. Such compositions may also contain a variety of additivesfor special purposes, such as hydrocarbyl triazoles for corrosionprotection of copper and copper alloys (EP-A-0 564 721).

[0005] There is a need to check the quality of the coolant solutionregularly to ensure problem-free operation. For the development of OATcoolants, organic acids were neutralized with alkali metal hydroxides(preferably sodium hydroxide (NaOH) or potassium hydroxide (KOH)) toobtain the inhibitor salts used in the new organic formulations, see forexample, U.S. Pat. Nos. 4,647,392; 4,851,145; and 4,759,864. It was soonrealized that an acid titration of an OAT solution could provideinformation on the total carboxylic acid inhibitor content. U.S. Pat.No. No. 5,366,651 shows in FIG. 1 some titration curves for combinationsof carboxylate

[0006] inhibitors with an organic pH buffer such as imidazole.

[0007] In order to evaluate the OAT coolant quality in the field, theend user needs to be able to check the amount of contamination withother coolants, as well as carboxylate inhibitor content.

[0008] The present invention provides an improved method and apparatusfor field testing and analysis of coolants and heat exchange fluids.

SUMMARY OF THE INVENTION

[0009] According to one aspect of the invention, there is provided atest method for determining the content of carboxylic acid-basedcorrosion inhibitors in a coolant or heat exchange fluid whichcomprises:

[0010] (a) placing a sample comprising a predetermined amount of thematerial to be tested in a titration vessel,

[0011] (b) stirring or otherwise agitating the sample while adding anacidic reagent at a constant rate,

[0012] (c) measuring the pH of the stirred sample while the acidicreagent is added,

[0013] (d) determining a first equilibrium point (EP 1) demonstrated bya first rapid drop in pH,

[0014] (e) continuing addition of acidic reagent and measuring the pHuntil a second equilibrium point (EP2), demonstrated by a second rapiddrop in pH, is reached, and

[0015] (f) determining the amount of carboxylic acid-based corrosioninhibitor in the sample from the amount of acidic reagent added betweenEP 1 and EP2.

[0016] Other aspects of the invention provide:

[0017] A method wherein the content of contaminant in the sample isdetermined from the amount of acidic reagent required to reach the firstequilibrium point.

[0018] A method wherein the amount of freezing point depressant in thesample is determined from the refractive index of the sample.

[0019] A method wherein the pH is determined by means of a calibratedelectrode in the titration vessel.

[0020] A method wherein at least one quantity selected from the observedvalues of pH, the amount of carboxylic acid corrosion inhibitor, theamount of contaminant, the refractive index, and the freezing point ofthe sample is displayed visually.

[0021] According to another aspect of the invention, there is providedan apparatus for conducting a test method as described above whichcomprises a titration vessel, first and second reservoirs for acidicreagent and waste neutralizing agents respectively, a first pump fortransferring acidic reagent from the first reservoir to the titrationvessel and a second pump for transferring waste neutralizing agent tothe titration vessel from the second reservoir, a stirrer for stirringsamples in the titration vessel, a pH electrode in the titration vessel,display means for displaying information determined by tests conductedin the apparatus, and electronic control means for controlling saidapparatus.

[0022] The present invention is directed towards a field- or laboratorytest technique to determine the quality of antifreeze/coolantor aqueousheat-transferor heat-exchangefluids. An apparatus and method aredescribed by means of which it is possible to measure the content ofcarboxylate corrosion inhibitors in OAT coolants or heat exchangefluids, such as Havoline Extended Life Coolant (XLC) (Havoline productsavailable from Texaco Inc.), or heat exchange fluids containing HavolineExtended Life Corrosion Inhibitor (XLI) or mixtures thereof. In onepreferred aspect of the invention, the method is used to also measurethe contamination level in XLC contaminated by traditional borate orphosphate containing coolant or with the more recently introduced hybridOAT-traditional coolants such as Havoline Antifreeze Coolant (AFC).Alternatively, it is of course possible to make calibrations for otherOAT coolants.

[0023] In another aspect of the present invention, the measurement ofcontamination level, carboxylate corrosion inhibitor content is combinedwith a measurement of the pH of the test solution.

[0024] In yet another preferred aspect of the invention, themeasurements of contamination level, total carboxylate inhibitor contentand pH are combined with a refractometric determination of the freezingpoint of the test solution.

BRIEF DESCRIPTION OF THE FIGURES

[0025] The invention will be further described with reference to theaccompanying Drawings in which:

[0026]FIG. 1 is a graphical plot showing the effect of the meteredaddition of acid upon the pH of aqueous solutions (Volume HCl2N,m 1) ofcertain commercial OAT coolants.

[0027]FIG. 2 is a graphical plot showing the effect of the meteredaddition of acid upon the pH of aqueous solutions (Volume HCl2N,ml) ofmixtures of commercial OAT coolants.

[0028]FIG. 3 is a graphical plot showing the effect of the meteredaddition of acid upon the pH to aqueous solutions (Volume HCl2N,ml) ofborax and silicate inhibitors.

[0029]FIG. 4 is a graphical plot of carboxylic acid content (V₂-V₁ incm³) and equilibrium points (percent concentration) for a carboxylicbased coolant.

[0030]FIG. 5 shows a graph of the refractive index of systems containingdifferent percentages (Vol. %) of monoethylene glycol.

[0031]FIG. 6 is a schematic view of one embodiment of apparatusaccording to the invention.

[0032]FIG. 7 is a perspective view of one embodiment of the apparatusaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] This invention relates to a method and apparatus for testing thequality of engine coolants and heat-exchange fluids containing long lifeorganic corrosion inhibitors, comprising alkali metal, ammonium or aminesalts of carboxylic acids. Such coolants are usually referred to asOrganic Acid Technology (OAT) coolants or heat-exchange fluids. Moreparticularly, this invention relates to a field test, requiring aminimum of operator interaction optionally determining, separately orcombined in one test sequence, values for carboxylate inhibitor content,contamination level, pH and frost protection of the tested coolant orheat-exchange fluid.

[0034] The corrosion inhibitors used in engine coolants are inorganicand/or organic compositions which can be considered as chemical bases.Generally a coolant has a pH of approximately 6.5-9.5 in order to ensureadequate protection ol the metals used in engines and cooling andheat-exchange systems. Since the corrosion inhibitors are chemicalbases, an analytical technique such as an acid-base titration withhydrogen chloride can be used for the determination of the inhibitorconcentrations. The pH of the used coolant provides information onfurther suitability for use. pH values that are too high or too low maybe detrimental to some engine- or heat-exchange system materials.Finally, if applicable, a check on the freezing point will provideinformation on frost protection.

[0035]FIG. 1 shows the difference between the acid-base titration of ahybrid coolant containing borate, silicate and benzoate and carboxylatebased inhibitors. These are Havoline Antifreeze Coolant (hereinafterindicated by the abbreviation AFC) and a fully carboxylate basedtechnology Havoline Extended Life Coolant (hereinafter indicated by theabbreviation XLC). FIG. 1 shows the effect upon pH of the addition of214 hydrochloric acid (HCl2N) to eight samples showing various amountsof AFC and XLC in deionized water (DIW). Four curves show respectively10%, 20%, 30% and 50% AFC in DIW. The other four curves showrespectively 10%, 20%, 30% and 50% XLC in DIW.

[0036]FIG. 2 shows the effect upon pH of metered addition of 2Nhydrochloric acid to different mixtures of AFC and XLC. The curves showrespectively 5%, 10%, 15%, 20%, 30%, 40% and 50% of AFC in XLC; onecurve shows pure AFC.

[0037]FIG. 3 shows the effect upon pH of metered addition of 2Nhydrochloric acid for solutions of borax and silicate. The influence onthe positioning of the first equilibrium point is clearly shown. Thismakes it possible to evaluate unequivocally the amount of traditionalinhibitors in a titrated coolant sample, and consequently the amount ofcontamination.

[0038] In the titration curves of the hybrid coolant with hydrogenchloride, two distinct equilbrium points (EP) can be observed. Thetitration curve for the carboxylate based, XLC, coolant shows a firstequilibrium point (EP1) at approximately pH=7.0, but only a small amountof acid shows consumed at this point. This may be compared with thehybrid coolant, AFC, which already shows a considerable consumption ofacid at EP 1. Up to EP1, all silicate- and borate-based inhibitors areneutralized by the acid. Between EP1 and the second equilibrium pointEP2 carboxylates are converted into the corresponding organic acids.This can be also derived from the acid-base dissociation constants forthe inhibitors silicate (NaHSiO₃ PK_(a)=9.2) and typical aliphaticorganic acids (RCOOH pK_(a)=4.5).

[0039] These titration curves make it possible to estimate the amount oftraditional inhibitors used in a titrated coolant sample, this can bederived from the volume of acid consumed at EP 1. In addition, the shapeof these titration curves indicated that the amount of carboxylates canbe measured from the added acid volume difference between EP1 and EP2.

[0040] Experiment has demonstrated a linear correlation between theorganic acid concentration used in the Texaco coolant Havoline XLC andthe difference between the volume of acid added (in cm³) at the secondequilibrium point (V2 at pH 3) and the volume added at the firstequilibrium point (V1 at pH 7). This is illustrated below in the Tableand graphically in FIG. 4. TABLE % XLC VI (cm³) V2 (cm³) Measured V2 −V1 (cm³) 10 0.0275 0.74 0.7125 20 0.0545 1.46 1.4055 30 0.087 2.17 2.08350 0.2075 3.58 3.3725

[0041]FIG. 4 shows the correlation between the carboxylic acid contentsand the measured acid volumes added between the first and secondequilibrium points. It will be seen that the data points representingV1-V2 for the four percentage concentrations lie in a straight line.

[0042]FIG. 6 shows one possible preferred embodiment (in schematicfashion) of an apparatus according to the invention for measuring thecontamination levels in OAT, the total carboxylate content, andoptionally, the coolant pH and extent of frost protection.

[0043]FIG. 7 shows a perspective view from above and one side of oneembodiment of an apparatus according to the present invention.

[0044] One embodiment of apparatus according to the invention is showndiagrammatically in FIG. 6. The embodiment shown in FIG. 7 uses the samereference numerals as in FIG. 6 to identify functionally similarelements. As such, a separate description of the elements of FIG. 7 isomitted for brevity.

[0045] The apparatus comprises a titration vessel (1), a meteringburette (not shown) for transferring a metered sample of coolant to thetitration vessel, a pH electrode (9), a first reservoir (2) for acidreagent and a second reservoir (3) for a neutralizing agent, forneutralizing titrated samples after testing. A first metering pump (4)is provided for transferring metered additions of reagent acid from thefirst reservoir (2) to the titration vessel (1), by way of tubes (6, 6a). A second metering pump (5) is provided for transferring neutralizingagent from the second reservoir (3) to the titration vessel (1) by wayof tubes (7, 7 a), after the pH and any other measurements have beencarried out. Means such as a magnetic stirrer (8) are provided in orderto obtain good mixing of the test solution. If desired, another mixingdevice can be employed instead of the magnetic stirrer, such as a mixeror homogenizer to mix, stir or otherwise agitate the test solution.

[0046] A pH electrode (9) and optionally a refractometric probe (14) areprovided for determining the pH and refractive index of the contents ofthe titration vessel (1). Electrode (9) and probe (14) are connected toa control unit (11) containing electronics including a start button(12), an analog signal treatment device (13), an analog to digitalconverter (20), and a microcontroller, or other type of computer orprocessor (30), with program software to treat the signals fromelectrode (9), to and from the metering pumps, and to an alphanumericaldisplay (10) to show the results and test comments. Display (10) can be,for example, a liquid crystal display (LCD). Optionally the electronicsalso contain means or signal treatment to and from the refractometricprobe (14), and software for signal processing of pH reading anddetermination of the freezing point based on a refractometricmeasurement, indicating the content of freezing point depressant. Thedisplay (10) can provide customized messages according to the results ofthe test.

[0047] Means are also provided in terms of software and standardsolutions to calibrate the pH measurement and optionally the measurementof refractive index.

TITRATION PROCEDURE

[0048] The following titration procedure is carried out in accordancewith one embodiment of the invention on coolants in order to determinepossible contamination with traditional corrosion inhibitors and theamount of carboxylate inhibitors present in a coolant sample:

[0049] 1. A fixed volume, for example 25 ml of coolant, is taken out ofan engine, radiator or expansion vessel of the cooling or heat-exchangesystem with a fixed metering pipette, and transferred to the titrationvessel (1), e.g. with a syringe.

[0050] 2. The calibrated pH-electrode (9) is brought into the titrationvessel and acid reagent is pumped into the vessel throughpolytetrafluoroethylene(PTFE) tubes (6, 6 a) connected to the firstreservoir (2) containing hydrogen chloride solution at a fixedconcentration (for example 2N HCl).

[0051] 3. The start button (12) is activated to begin the measuringprocess. The liquid is stirred for instance by a magnetic stirrer (8).

[0052] 4. A wait cycle, e.g. of 20 seconds, starts for stabilizingpurposes. The pH of the test solution is recorded in the memory of thecontroller. If the initial pH is below a limited value acceptable forthe coolant, the process stops and a warning message is displayed on theLCD. Optionally, the initial pH is shown on the LCD screen.

[0053] 5. If the pH is above the limited value accepted for the coolant,the microcontroller generates a pulsed signal to the first metering pump(4) and acidic reagent is dosed at an exact rate into the titrationvessel (1). A typical addition rate is 1 cm³/min.

[0054] 6. The microcontroller keeps track of the measured pH and thedosed amount of reagent.

[0055] If the pH reaches the first equilibrium point, corresponding to apH of 7.0, the quantity of reagent acid that has been added is storedand used to calculate the “Contamination level”. This contaminationlevel is displayed on the LCD screen. If this level exceeds a limitvalue which is unacceptable for further use of the coolant(contamination limit), the process is stopped and a warning message isdisplayed.

[0056] 7. If this contamination limit is not reached, the systemcontinues and starts counting the amount of acid reagent dosed, andstores it in a second memory. The process continues until the pH reachesthe second equilibrium point at pH 3. At this point the microcontrollerstops the activating pulse signal to the metering pump (4). The recordedquantity of reagent dosed between the contamination point and theinhibitor level point is used to calculate the actual carboxylatecorrosion inhibitor content. This value (in % reading) is displayed onthe LCD screen.

[0057] 8. The microcontroller then starts the generation of anactivating pulse signal to the second metering pump (5), and acontrolled amount of caustic waste treatment fluid is pumped from thesecond reservoir (3) through tubes (7,7 a), which may also be formedfrom PTFE, into the titration vessel (1). This continues until thesolution reaches a fixed pH value. The test fluid can then be removedand disposed of, together with normal coolant waste.

[0058] The microcontroller can, for example, be a BS2-IC model made byParallax, Inc. The pumps can, for example, be MLP-200 and/or MLP-50models made by Tagasago Electric, Inc.

[0059] According to an optional preferred embodiment of the invention,the content of freezing point depressant is measured at step 4. This canbe done by means of refractometric probe (14). This probe may consist ofa prism made of material with high refractive index (for instance flintglass with refractive index n=1.88), a near infrared light emittingdiode (LED) and a radiation detector (e.g. a phototransistor orphotodiode). Means are provided to reduce the influence of incidentradiation (e.g. a near infrared transmitting filter on the detectionside). A pulse technique is used to reduce aging of emitters anddetectors. Using this pulse technique, dark current and incident lightcompensation makes the measurements more reproducible then conventionalrefractometric techniques. The amount of infrared radiation internallyreflected within the prism will be a function of the refractive index ofthe test solution in which the prism is immersed. The microcontrollercorrelates the measured refrative index for the used medium (forinstance an aqueous solution of ethylene glycol). The freezing point isthen displayed on display (10).

[0060]FIG. 5 shows the results of measuring the percentage: ofmonoethylene glycol by the refractive index methodology described above.

[0061] The apparatus can be easily modified to calculate and display thecontamination levels and carboxylate contents for coolants other thanXLC and AlFC. Since this measurement is virtually independent of thebase fluid, it can be used in aqueous glycol-free solutions or inmixtures of water and glycol and/or other freezing point depressants.Accordingly, the present invention is not limited to any particularcoolant, heat-exchange fluid, or base fluid.

1. A method for determining a content of a material, comprising: (a)agitating a sample comprising a predetermined amount of the materialwhile adding an acidic reagent at a constant rate, (b) measuring a pH ofthe agitated sample while the acidic reagent is added; (c) determining afirst equilibrium point (EP1) demonstrated by a first rapid drop in pH;(d) continuing addition of the acidic reagent and measuring the pH untila second equilibrium point (EP2), demonstrated by a second rapid drop inpH, is reached; and (e) determining an amount of carboxylic acid-basedcorrosion inhibitor in the sample from an amount of acidic reagent addedbetween EP1 and EP2.
 2. A method according to claim 1, furthercomprising: (f) determining a content of a contaminant in the samplefrom an amount of acidic reagent required to reach the first equilibriumpoint.
 3. A method according to claim 1, further comprising: (g)determining an amount of freezing point depressant in the sample and afreezing point from a refractive index of the sample.
 4. A methodaccording to claim 1, wherein the pH is measured using an electrode. 5.A method according to claim 3, wherein the refractive index of thesample is measured using a refractometric probe.
 6. A method accordingto claim 1, wherein the EP1 is at a pH of about
 3. 7. A method accordingto claim 1, wherein the EP2 is at a pH of about
 7. 8. A method accordingto claim 1, further comprising: (f) displaying the pH.
 9. A methodaccording to claim 2, further comprising: (g) displaying the pH; and (h)displaying the content of the contaminant.
 10. A method according toclaim 3, further comprising: (g) displaying the pH; and (h) displayingthe refractive index.
 11. A method according to claim 10, furthercomprising: (i) displaying the freezing point.
 12. A method according toclaim 2, further comprising: (g) determining an amount of freezing pointdepressant in the sample and a freezing point from a refractive index ofthe sample.
 13. A method according to claim 12, further comprising: (h)displaying at least one quantity selected from the group consisting ofthe pH, the content of the contaminant, the refractive index, and thefreezing point.
 14. A method according to claim 1, wherein the steps arecarried out using one apparatus.
 15. A method according to claim 1,wherein the steps are carried out using an apparatus comprising aprocessor.
 16. An apparatus for determining a content of a materialcomprising: a vessel configured to contain a sample of the material; afirst reservoir configured to contain a reagent; a second reservoirconfigured to contain a treatment fluid; a first pump configured totransfer reagent from the first reservoir to the vessel; a second pumpconfigured to transfer treatment fluid from the second reservoir to thevessel; a pH electrode configured to measure a pH of the sample; and ameans, coupled to said pH electrode, for controlling said first pump andsaid second pump responsive to the measured pH.
 17. The apparatus ofclaim 16, further comprising: a means, coupled to the vessel, foragitating the sample.
 18. The apparatus of claim 17, wherein said meansfor agitating comprises a stirrer.
 19. The apparatus of claim 16,further comprising: a display connected to said means for controlling.20. The apparatus of claim 19, wherein said display is a liquid crystaldisplay.
 21. The apparatus of claim 16, wherein said means forcontrolling comprises a processor.
 22. The apparatus of claim 16,wherein said means for controlling is a microcontroller.
 23. Theapparatus of claim 16, further comprising: a refractometric probeconnected to said means for controlling.
 24. The apparatus of claim 16,further comprising: a means, connected to said means for controlling,for measuring a refractive index of the sample.
 25. The apparatus ofclaim 16, further comprising: an analog to digital converter configuredto treat a signal from said pH electrode.
 26. The apparatus of claim 16,wherein said means for controlling comprises: an analog to digitalconverter configured to treat a signal from said pH electrode.
 27. Theapparatus of claim 23, further comprising: an analog to digitalconverter configured to treat a signal from said pH electrode and asignal from said refractometric probe.